Propeller assemblies typically include multiple blades mounted to a hub, which is rotated by the engine. The blades can be line-removable and retained to the hub so as to supporting operating loads, including a centrifugal force component that acts in a direction parallel to the longitudinal axis of the propeller blade. Modern retention systems use an assembly of bearings to retain the propeller blade to the hub assembly. Each blade root is retained within its own socket for rotation therein about a pitch change axis through use of the assembly of bearings. These bearings can be preloaded or not preloaded.
Historically, retention systems of non-preloaded propeller blades rely on the weight of the blades to ensure that they experience sufficient centrifugal loading when rotating during operation that rocking of the retention bearings does not occur. However, modern lightweight blades may not experience sufficient centrifugal loading to prevent the bearing elements on one side of the bearing from becoming unloaded under the influence of bending loads imposed upon the blade during operation. Consequently, larger and heavier parts can be necessary for the retention mechanisms.
It is known to preload the blade and the bearings in order to maintain their stability under high centrifugal and thrust forces experienced during operation. Further, additional preloading mechanisms can be utilized to compensate for loss of preload on the bearings due to wear. The preloading tensions the system and braces it against operational centrifugal and thrust forces. The inclusion of additional preloaded assemblies results in more complex replacement and maintenance of parts. Further still, such designs use grease within the hub as lubrication and the grease loses its lubricating properties over time, leading to more frequent maintenance.